Have you ever heard of anal fingering? It's exactly what it sounds like — putting a finger (or several) into someone's anus. And if you're considering anal sex.
My husband has recently started to insert his finger in my back I asked him if he wanted anal sex and that's why he was doing it, but he insists.
Slowly insert your lubed finger into the anus and curl your finger upward in a “ come hither” motion. Gradually increase the depth and speed.